Method and apparatus for making plastic lined continuously welded aluminum tubing



W. G. REYNOLDS S FOR MAKI Dec. 25, 1962 METHOD AND APPARATU NG PLASTICLINE CONTINUOUSLY WELDED ALUMINUM TUBING 5 Sheets-Sheet l Filed April20. 1959 Dec 25 1962 W. G. REYNOLDS 3 0 METHOD AND APPARATUS FOR MAKINGPLASTIC LINED 69763 CONTINUOUSLY WELDED ALUMINUM TUBING 3 Sheets-Shea?I2 Filed April 20, 1959 Il l: Il l INVENTOR. Wfl/fam Kejnu/ 5 BVM C W. G.REYNOLDS PARATUS Dec. 25, 1962 METHOD AND AP FOR MAKING PLASTIC LINECONTINUOUSLY WELDED ALUMINUM TUBING 3 Sheets-Sheet 3 Filed April 20,1959 s h @l m AW 8 m. IW n, l

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NVENTOR. Wil/fam G. Royal/JS www 3,06%,763 Patented ec. 25, 196.2

.ce alle@ ME'if-ll) AND AFFARTUS EGR MAKEN@ PLASTEC lLiNED CUNTENUUSLYWELDED ALUMHNUM TUBNG William G. Reynolds, Anchorage, Ky., assigner toReynolds Metals Company, Richmond, Va., a corporation of Delaware FiledApr. 2i), 219:39, Ser. No. 807,578 i3 Claims. (Cl. 29-429) Thisinvention is directed to a method of making plastic lined sheet metaltubing progressively and continuously.

Several methods and apparatus have been suggested in connection with themanufacture of multiple layer sheathed tubes or cables. For example, thepatents to Greenfield, 469,662; Witzenmann, 830,695; and Boetelink,2,758,3 66, disclose ways of placing a metal sheath around a tube.However, there is no disclosure how simultaneously to weld a seam of theouter metal sheath without unduly heating and injuring the internaltube, if such tube is made of flexible or plastic material.

The patents to Lavens, 570,256, and Garten, 2,745,778 disclose coaxialinner flexible tubes and outer metal sheaths, in which the relativediameters of the coaxial tubes are changed to secure the tubes together.However, there is no disclosure whereby the outer sheath can be seamwelded in a continuous operation with the methods disclosed in thepatents.

The patents to Munger, 2,417,881 and 2,440,725, disclose an innerplastic tube coaxial with an outer metal sheath, the inner tube beingexpanded, and both tubes being heated to a relatively low adhesiontemperature. However, this operation cannot be accomplishedsimultaneously with seam welding of the outer sheath, and also there isno way whereby the air between the outer tube and the inner tube may beeffectively removed throughout the length of a long tube while theplastic tube is being expanded.

The patents to ohnson, 1,794,902; Westlinning, 2,029,044; and Kinghorn,2,697,772 disclose methods whereby an insulated electric cable may becovered with a strip of sheet metal, and the strip seam welded aroundthe cable. However, these patents rely upon the fact that the electriccable is of a relatively solid nature, and this feature is relied uponfor the success of the operation.

No way of expanding a plastic tube within the sheath simultaneously witha seam welding operation is disclosed, in a manner to avoid damage tothe plastic tube by the ,'elding heat, and still accomplish adhesion ofthe tubes after the seam weld in a continuous manner.

All of the foregoing objections or shortcomings in connection with themanufacture of plastic lined tubing are overcome by this invention, aswill become apparent.

According to this invention, a novel method, and a novel apparatus forpracticing such method, are provided in which a metal sheet strip,preferably made of aluminum or an alloy thereof, is progressively foldedinto a relatively wide open seam tube. A flexible tube is progressivelyintroduced into such wide open seam tube and then the open seam tube isfurther folded into a more fully closed open seam tube. A zone ismaintained within such open seam tube in which the flexible tube ismaintained in relatively tight folded position away from the weldingheat by means extending through said open seam. The open seam is thenclosed and welded adjacent the above zone. A fluid under pressure isintroduced into the downstream end of the flexible tube, and thispressure is arrested adjacent the relatively tight folded condition zoneof the flexible pipe so the flexible tube is expanded outwardly againstthe metal tube to cause adhesion between the metal and flexible tube.

Because of this novel method and apparatus, it is possible continuouslyto make a plastic lined sheet metal tube very cheaply and eihciently.

This invention also relates to a method, apparatus, and product whereina plastic pipe is placed within .a sheet metal tube having relativelysmall or minute perforations which permit the air between the tubes toescape outwardly through the perforations while the plastic tube isbeing expanded against the inside wall of the metal tube. Such a tubemay be used with the perorations in their original condition when theenvironment of use is not harmful to the plastic pipe. The perforatedmetal sheet suiiiciently protects the plastic pipe against physical harmunder these conditions. However, if desired, the diameter of the outersheet metal tube may be reduced substantially to close the perforationsto a degree wherein, under more adverse conditions of use, substantiallyno harm can occur to the plastic pipe.

Other objects and features of this invention will become apparent as thedescription proceeds with reference to the accompanying drawings inwhich:

FIGURE 1 is a diagrammatic side view representation of an apparatus andmethod for processing plastic lined sheet metal tubing, in which theseam of the metal tube is gas or arc welded.

FIGURE 2 is a top plan View, on an enlarged scale, of a portion ofFIGURE 1.

FIGURE 3 is a vertical, longitudinal, cross-section of FIGURE 2.

FIGURE 4 is a transverse cross-section taken along the line 4 4 ofFIGURE 3.

FIGURE 5 is a view similar to FIGURE 1, in which the seam is inductivelywelded.

FIGURE 6 is an enlarged top view of part of FIG- URE 5.

FIGURE 7 shows part of FIGURE l, on an enlarged scale, showing howcertain features of FlGURE l, or sidnilirly of FIGURE 5, may be omitted,and others a e FIGURE 8 shows how a part of apparatus and method similarto that disclosed in FlGURES 1, 5 and 7 may be used with a perforatedsheet metal strip..

FlGURE 9 is a cross-section of a finished, or partially finished, tubeproduced by the method disclosed in FIG- URE 8.

FIGURE l0 is a diagrammatic side view representation of an apparatus andmethod for further processing the tubing disclosed in FIGURES 8 and 9.

FEGURE 1l is a cross-section of the final tube product of FIGURES 1through 7.

ln FGURE l through 4, a strip of sheet metal, preferably made ofaluminum or an alloy thereof, is indicated by the numeral 20 and isprogressively fed from the reel 21. It progresses or travels pastfolding means, such as rollers 24 and 25, by which the strip 20 isprogressively folded into a relatively wide open seam tube, indicated bythe numeral 20a. A flexible tube 28 is progressively introduced into theopen seam tube 20a at 29 from the reel 30, under the guidance of theroller 31.

The llexibe tube 28 may be a plastic tube, made preferably of athermoplastic material, such as polyethylene. The polyethylenepreferably is of the nature that remains relatively drm in temperaturesup to 300 or 400 F. lf the selected polyethylene does not becomeadhesive at these temperatures, it may be coated with a material whichdoes become adhesive at a lower temperature, or at these temperatures,and such material may be polyethylene having lower temperature adhesivecharacteristics.

Preferably, the flexible tube 28 is so wound around accenna the reel 3dthat air under pressure in said tube 28 may readily escape through theupstream end 28a of the tube 28. ln this manner, any substantial rise inair pressure is prevented on the upstream side of the tube 28, for apurpose hereafter to become apparent.

The tube a is progressively further folded by the rollers 34 into a morefully closed but still open seam tube Ztlb.

A relatively long, hollow shoe 4u is supported by the suction outletpipe 4l through the open seam of the tube Zitlb. If necessary, the shoepipe 4l partially reopens the seam of the metal tube Zlib as indicatedat in FGURE 2. The shoe 4t) is hollow, and semi-cylindrical intransverse section, as indicated in FlGURE 4, so that it maintains azone wherein the plastic tube 2S is maintained in a relatively tightfolded condition, as shown in FSURE 4, so that only a Very slight amountof air under pressure can pass through this zone from the downstreamside of tube 2S to the upstream side of the tube Z.

The shoe 4t) is provided with an air inlet at 43 so that air within thetube Zub is withdrawn through the opening 43 and tlows through the shoe4d and suction outlet 4l to a suction pump, not shown, therebymaintaining the zone adjacent the shoe 4t) in relatively cool condition,and particularly the Flexible tube 2S and the lower part of the metalstrip 2%.

Adjacent to, or above, the zone of the shoe 4t), the open seam of themetal strip 2% is closed by the rollers 4o, and the seam is welded by awelding head 4t-3 which operates by gas or electric arc. if desired,cooling air may be introduced by the nozzle 50 under the hood 52 to coolthe metal tube after the welding operation. The shoe 4Q may have anextension 48u, shown in FIGURE 7, which is sutliciently long to permitsubstantial cooling of the seam weld. This extension 46a may also extendupwardly to contact the upper part of the tube on both sides of theseam, to brace the shoe 4@ against upward movement at that end.

lf desired, a iluid valving and/or flexible tube spreading device 54 maybe introduced into a downstream side of the flexible tube 2S. Forexample, this device may have a blunt front end 55 and one or morecircular fins 56 which are adapted to valve the iiuid or air underpressure on the downstream side of the tube 28 and to prevent anysubstantial travel of such air past the device 54 into the upstream sideof the tube 2S. The device 54 tends to travel leftward in FXGURES l, 2and 3, being propelled by air under pressure delivered by the pump 58into the downstream end 66 at the center of the reel 62 on which thecompleted multiple layer tubing is wound. The device 54 is introducedinto the tube 28 before attachment of the pump discharge pipe 63 to theend `tt of the tube 2S. Suitable rotary seal connections are providedbetween the pipe o3 and the plug in the end 60 as is obvious. Theleftward travel of the device 54 is arrested by the shoe 4G, or itsextension 49a, so the device 54 cannot pass the tight folded zone oftube 23. Any slight amount of air which may pass the device 54 and thetightly folded zone of the tube 23 around the shoe dll is free to travelup the tube 28 and out at the upstream end 28a of the tube 2S, thus tomaintain a relatively low air pressure within the upstream side of thetube 23, without materially unfolding the upstream portion of the tube28.

Preferably, a heating zone d6 is provided through which the tubes Zttlband 2S travel on the way from the welding apparatus to the reel 62.rIbis heating zone is maintained at a sufciently high temperature toheat the tubes 2Gb and 28 to a temperature sufficient to cause adhesionbetween the flexible tube 23 and the tube Zlib. This zone may be heatedby gas, electric resistance, or electric inductance heaters, and may bethermostatically controlled in response 'to the temperature of tubeZtlb, or any other temperature, to maintain the desired temperatureconditions. 'he pressure of the tluid or air within the downstream sideof the tube 23 aids in insuring outward pres sure in the tube Z8 toproduce the correct adhesion betv een the tubes Z8 and Ztlb at theheating Zone 65.

The spreading device 5d may be a ball of metal or the like and of theproper diameter, in lieu of the device il lustrated.

ln the embodiment shown in JGURES 5 and 6, all of the elements indicatedthereon by numbers below lG operate substantially in the same manner,and have the same construction, as in FGURES l to 4. However, thosewhich are numbered in FGURES 5 and 6 above the numeral l0() and belowthe numeral 2S() operate more or less differently from elements inFIGURES l to 4, in a manner now to be described.

rEhe shoe 14) and shoe pipe E41 in FGURES 5 and 6 have substantially thesame shape as the shoe itl and shoe pipe 4d in FGURES l to 4, exceptthat the shoe it is made of a rigid electrically insulating material inwhich electric current cannot be materially induced or transmitted.Likewise, the suction tube lttl is substantially of the same shape astube 4l in FlGURES l to 4, except that it also is made of the samelinsulating material as the shoe tdt). ln addition, plates 14T; ofmetal, or the like, are secured on each side of the tube Mil, and theseplates M2 are electrically insulated from each other. They prevent theedges of the tube Zub from cutting into the insulating material of thetube M1, but do not short circuit the induced currents in tube 21311.

A pair of rollers lo causes the seams 12tlg and 12u11. gradually toconverge and meet at lj in abutting relationship adjacent the rollers146. A high frequency .inf duction coil 148 is placed around the tube2Gb and around the zone on which the edges 12tlg and liti/z areconverging, as shown in FlGURE 6. The induction coil t may be of anywell known type and may operate on the well known induction weldingprinciple, which is described, or example, in the patent to inghorn No.2,697,772, patented December 2l, 1954. The coil 14S causes an inducedwelding current to tlow and to produce a very intense heat atapproximately the point Ztij where the seam edges Ztig and 126.11 meet.This produces a seam weld without appreciably heating the remainder ofthe tube 201'; to a harmful temperature. The shoe 46 maintains theliexible tube 28 in the lower part of the tube Zub away from the weldingheat during the welding operation in the same manner as in FIGURES 1 to4. Thereafter, the tube 'b may be operated upon by the members 5t), 52,etc., substantially as in FGURES l to 4 and may be wound around the reel62, with air pressure added to the iiexible tube by a pump 5Ssubstantially in the same manner as in FGURES l to 4. The details whichare substantially identical with those in FGURESl l to 4 are not furtherdescribed.

FIGURE 7 shows specifically how certain features ofv FGURES l-4 may beomitted and/or others added..- It is also obvious that these featuresmay be omitted and@ added to the embodiment shown in FGURES 5 and 6,without the necessity of repeating the illustration. fn FIGURE 7, theflexible tube spreading device 54. of FG- URES l-4 and 5 and 6 may beomitted, and in lieu thereof the squeezing action of the shoe 41B, or34d, is made suicient to prevent any substantial harmful leakage ofcompression air from the downstream side (right hand side in FIGURESl-7) of t e tube 28 to the upstream side. Any small amount of air thatdoes leak past the zone of shoes 4o or is allowed to escape withsutlicient rapidity through the upstream side of the tube 28 and.through the upstream end 23a without substantially uit-- folding thetube 2S on the upstream side. Otherwise, the elements correspondingthereto which are illustrated in FIGURES l-6 may operate as previouslydescribed with the complete systems which are illustrated in FIGURES land 5.

Another feature which is illustrated in FGURE 7, and which may be addedto corresponding elements in either` sheaves FGURES l4 and/or FIGURES 5and 6, is that an extension lita may be added to the right-hand end ofthe shoe du, or shoe lfitl, which is suihciently long to permit a Verysubstantial cooling of the seam Weld. This eX- tension fitta may alsoextend upwardly to contact the upper part of the tube Zlib on both sidesof the seam to brace the shoe against upward movement at that end. Abreak in FGURE 7 is shown at itil? to indicate that the extension ibamay be ot considerable length. lt is thus understood that thecorresponding extension in FIGURES 5 and 6 will be of the sameinsulating material as the shoe whereas such extension @da in FEGURES 1Jmay be of metal or any other desired material, since no electriccurrents are induced in the structure of FIGURES l-l.

in the embodiments of FGURES 8-10, a perforated tube 225th may be madefrom a perforated metal sheet, preferably of aluminum or an alloythereof, substantially the same apparatus and steps disclosed inconnection with FIGURES 5 and 6 (or FIGURES l-4) except that thepressure pump 255i is not operated while the tubes 220i: and 22S,corresponding to tubes Zb and 23, are being wound around the reel 262,which is shown in FIGURE l0. instead, the flexible tube 22d is allowedto remain in collapsed condition while being wound around the reel Theshoe Edil, similar to shoe le@ of FIGURES 5 and 6, may be incorporatedin the apparatus of FIGURE 8, but need not be of the same lateral andlongitudinal extent and need not press downwardly as tight as in FIG-URES 5 and `6. However, it should be sulhcient to maintain the foldedtube 22d in the lower part of the tube Accordingly, the tube 241 and theshoe 2d@ are illustrated in FIGURE 8 as not producing the same amount ofseam spreading action as shoe illlti and tube fidi in FGURES 5 and 6,but a substantial amount of spreading is produced, which is suiiicientto prevent the flow oi current between the seam edges Zg and 22611 untilthe tube 22d/b reaches the joining point at 220i, as is well known inconnection with the induction Welding principle. The rollers operatesubstantially in the same manner as the rollers ido in FiGURES 5 and 6.No heating zone corresponding to heating zone 66 of FlG- URE 5 is usedbetween the apparatus or FIGURE 8 and the reel of Fl'GURE 10.

The plastic tube 22E may be substantially in the same condition as thetube 28 in FlGURES 5 and 6 through the seam welding operation. However,it is not spread out by the spreading device S4, or by pressure from thepump of FIGURE 5, but is allowed to remain in collapsed and unheatedcondition until the tubingy is wound completely on the reel 25?..

Thereafter, the tubes 22611 and 228 are unreeled from the rcel 252, asillustrated in FlGURE l0, for example, by being pulled by a set ofrollers 27@ or by a reel 362. rlhe rollers 27d may be diameter reducingrollers if desired, or merely frictional pulling rollers which producepractically no diameter' reduction of the tubes 22) and rhe end 228:1 ofthe flexible pipe 228 is closed as by a plug 272 which is inserted inthe end 223g of the pipe 22S and is clamped by a strap 27d around bothof the pipes 22S and 12b. A heating means 266, which may be a gasheating oven, or an electric heating oven of resistance or inductiontype is provided to heat the pipes 22% and 223 to the desired adhesiontemperature. Air under pressure is supplied by the pump to the end Edilof tube 228, and the two tubes 228 and 251% are caused to adheretogether as they are heated in the heating zone 266 by the pressureinside or the pipe 228. if desired, the completed pipe may be woundaround the reel 3o2.

The completed tubing produced by the apparatus shown in FGLRES S and l0has a cross-section diagrammatically the sane as shown in FlGURE 9except that the openings may actually be of smaller diameter and may becloser together relatively to the diameter of the tubing than isdiagrammatically illustrated in FlGURES 8 and 9.

The total area of the openings ZS@ is sutccient to allow any air in tube22%, which is present while the tubing 228 is in collapsed condition, toescape through the openings 230 by the time that the tubing reaches anadhesion ternperature in the heating zone 266. The iinal escape of theair through the openings Zli may continue for a certain length of travelof the tubing, while still hot, beyond the heating zone 26d, if desired.The pressure produced by the pump 258 as the tubes unwind from the reel262 spreads the tubing outwardly until it is completely in contact withall of the inside of the tube 22%. The length of the heating zone 265may be considerable, so that substantially all of the escape of the airthrough the openings 283 can take place before the tubes leave the g isbeing heated and renused to reduce the diameter of the tubings Zlibafter the tubing has been blown outwardly. This causes the openings Qito become smaller and to produce a certain amount or gripping action or"the tube with respect to the tube iii/iti.

The 362 alone may be used to pull the pipes 212% and through the heatingzone 26o trom the reel 26?.. Under these con l ions, if the diameterreduction is not desired, the rollers may be omitted and all of thepulling action be produced by the reel 362.

Also, if desired, the reel in FEGURE l0, or a plurality of reels may beplaced in an oven 37d where the tubes 22de and may be sl .yly heated toany desited temperature which may be as high as the adhesiontemperature. rhe end or ends 228e of the tube or tubes 228 may beplugged, as indicated at 272 and 274 within or just outside the oven37d. The pump 253 may be connected to the end or ends Ztili of such tubeor tubes 223 and air under pressure may be applied to the tubes. Thereel or nay remain in the oven B7@ while the tube or tubes 228 expandand adher.v to the interior surface or surfaces of the tubes 22% whileair in the tubes 22d/5 escapes, while in the oven 57d, through theperorations 23d. 'he tubes may then be unreelcd and be reeled on otherreels 3&3, or the reels may be used for shipment of the tubes.

The tubing as disclosed in FIGURES 8 to l@ may be used without reductionof diameter, if the size of the openings 2id@ is sufficiently small toprotect the tubing 228 from harm from the medium ea; ected to surroundthe tubing 22M, lIhe diameter' may be reduced where it is desired tomalte the openings smaller in order to afford greater protection to thetubing 15Std. The original diameter of the opening may be suiiicientlysmall that they are substantially closed by the tube diameter reducingrocess herein described with respect to FTGURE il),

Under certain conditions, the periorations in tube Zlib may be a seriesof groups of relatively large openings in spaced zones along the lengthof the tube 2120i; while the intermediate parts of the tube are notperforated These zones spaced apart selected distances so the airbetween the tubes and 2.23 can escape through said large openings, andrelatively short unperforated tubes may be out between the zones oflarge openings. These short tubes may be used as short, plastic lined,unperforated sheath tubes where long tubes are not necessary.

FiGURE ll shows the crosssection of the plastic lined tubing which isproduced by the apparatus and method disclosed as in liGURES l through7.

While the form of the invention now preferred has been disclosed, asrequired by statute, other forms may be used, all coming within thescope of the claims which follow.

Whatl claim is: i

l. An apparatus for continuously forming multiple layer tubingcomprising: means for progressively folding a sheet metal strip into anopen seam tube; means for progressively introducing a exible, resilienttube into said open seam tube said tiexiblc tube being formed of amaferial that is not capable of withstanding a certain temperature; ashoe adapted to be supported through saidV open seam and adapted to holdsaid Flexible tube in col-- lapsed condition away from said seam; meansfor closing` and welding said open seam adjacent said shoe said weldingmeans being of a type that produces said certain temperature that woulddamage said flexible tube if said Ilexible tube were disposed adjacentsaid seam; a flexible tube spreading device adapted to be placed in saidflexible tube on the discharge side of said shoe; and means forintroducing a fluid under pressure into the downstream end of saidilexible tube to expand said flexible tube between said downstream endand the proximity of said shoe by the action of said device.

2. An apparatus for continuously forming multiple layer tubingcomprising: means for progressively folding a. sheet metal strip into anopen seam tube; means for progressively introducing a vdexible,resilient tube into said open seam tube, said ilexible tube being of amaterial that is not capable or" withstanding a certain temperature; ashoe adapted to be supported through said open seam and adapted to holdsaid flexible tube in collapsed condition away from said seam; means forclosing and welding said open seam adjacent said shoe said welding meansbeing of a type that produces said certain temperature that would damagesaid flexible tube if said flexible tube were disposed adjacent saidseam; and means for introducing a iluid under pressure into thedownstream end of said flexible tube to expand said llexible tubebetween said downstream end and the proximity of said shoe.

3. An apparatus for continuously forming multiple layer tubingcomprising: means for progressively folding a sheet metal strip into anopen seam tube; means for progressively introducing a flexible,resilient tube into said open seam tube, said flexible tube beingfor-med of a material that is not capable of withstanding a certaintemperature; a shoe adapted to be supported through said open seam andadapted to hold said ilexible tube in collapsed condition away from saidseam; means for closing and welding said open seam adjacent said shoe,said welding means being of the type that produces said certaintemperature that would damage said flexible tube if said flexible tubewere disposed adjacent said seam; means for introducing a fluid underpressure into the downstream end of said flexible tube to expand saidflexible tube between said downstream end and the proximity of saidshoe; and means for heating said metal tube on the downstream side ofsaid shoe to cause adhesion between said metal tube and tiexible tube.

4. A method for continuously forming multiple layer tubing comprising:progressively folding a metal sheet strip into a relatively wide openseam tube; progressively introducing a flexible, resilient tube intosaid wide open seam tube, said ilexible tube being formed of a materialthat is not capable of withstanding a certain temperature; progressivelyfurther folding said strip into a more fully closed open seam tube;folding and maintaining said flexible tube within a zone in relativelytight folded condition away from said seam; closing and welding saidseam adjacent said Zone with a welding means that produces said certaintemperature that would damage said ilexible tube if said flexible tubewere disposed adjacent said seam; introducing a valving, spreadingilexible tube expander into the downstream end of said flexible tube;and introducing a fluid under pressure into said downstream end of saiddexible tube behind said expander to expand said flexible tube betweensaid downstream end and the proximity of said Zone with the aid of saidexpander.

5. A method for continuously forming multiple layer tubing comprising:progressively folding a metal sheet strip into a relatively wide openseam tube; progressively introducing a ilexible. resilient tube intosaid wide open seam tube, said exib-le tube being formed of a materialthat is not capable of withstanding a certain temperature;

progressively further folding said strip into a more fully closed openseam tube; ioldin7 and maintaining said ilexible tube within a Zone inrelatively tight folded condition away from sai seam; closing andwelding said seam adjacent said zone with a welding means that producessaid certain temperature that would damage said flexible tube if saidflexible tube were disposed adjacent said seam; and introducing a fluidunder pressure into said downstream end ci said ilexible tube to expandsaid flexible tube between said downstream end and the proximity ot saidzone.

o. A method for continuously forming multiple layer tubing comprising:progressively folding a metal sheet strip into a relatively wide opentube; progressively introducing a flexible, resilient tube into saidwide open semq tube, said ilexible tube being formed of a material thatis not capable ot withstanding a certain temperature; progressivelyfurther folding said strip into a more fully closed open seam tube;folding and maintaining said flexible tube within a zone in relativelytight folded condition away from said seam; closing and welding saidseam adjacent said one with a welding means that produces said certaintemperature that would damage said iiexible tube if said flexible tubewere disposed adjacent said seam; and introducing a 'iluid underpressure o said downstream end of said flexible tube to expand saidFlexible tube between said downstream end and the proximity of said zoneand heating said metal tube on the downstream side of said zone toprovide adhesion between said metal and tiexible tubes.

7. An apparatus for continuously forming multiple layer tubingcomprising: means for longitudinally feeding a sheet metal strip; meansfor partially folding said strip into an open seam tube; means forfeeding a flexible, resilient, plastic tube into said open seam tube,said plastic 'tube being capable or" withstanding a certain temperature;means for folding and collapsing said tube away from said seam; meansfor closing the seam of said open seam tube; welding means for weldingsaid closed seam while maintaining said collapsed plastic tube spacedfrom said closed seam, said welding means being of the type thatproduces said certain temperature that would damage said plastic tube ifsaid plastic tube were disposed vadjacent said seam; means forintroducing fluid under pressure adjacent the downstream end of saidplastic tube; and blocking means for blocking said fluid under pressureadjacent said welding means.

8. An apparatus according to claim 7, in which said welding meansincludes a shoe in said open scam tube supported by an extension passingthrough said open seam.

9. An apparatus according to claim 7, which includes means for heatingsaid tubes on the downstream side of said welding means.

l0. An apparatus according to claim 7, in which said welding meansincludes a shoe in said open seam tube and a supporting extensionextending through said open seam made of electric insulating material,and a high frequency inductance coil adjacent said shoe.

11. An apparatus according to claim 7, in which said welding meansincludes a shoe in said open seam tube, a supporting extension extendingthrough said open seam and a welding head adjacent said shoe.

l2. An apparatus according to claim 7 in which said blocking meansincludes a valving and spreading device.

13. A method for continuously forming multiple layer tubing comprising:progressively folding a metal sheet strip into a relatively wide openseam tube; progressively introducing a flexible, resilient tube intosaid wide open seam tube, said flexible tube being formed of a materialthat is not capable of withstanding a certain temperature; folding andmaintaining said llexible tube within a zone in relatively tight foldedcondition away from said seam during the welding thereof; welding saidseam along said zone while said flexible tube is held away from saidseam with a welding means of a type that produces said certaintemperature that would damage said exibla tube if said exib1e tube weredisposed adjacent said seam; and expanding said exible tube after saidseam has been We1ded.

v'itzenmann Sept. 11, 1906 Westlinning Ian. 28, 1936 10 Munger May 4,Kimble Aug. 26, Kinghorn Aug. 20,

FOREIGN PATENTS France Mar. 2l, France Dec. 1, Great Britain Aug. 25,

